1. Field of the Invention
This invention relates to an improvement in double-block cumulative multi-draft wire drawing machines.
2. Description of the Prior-Art
In wire drawing machines of the above-mentioned type, the wire is drawn through a succession of stations. Each station includes upper and lower blocks and a spinner carrying a transfer sheave. The blocks and spinner are rotatable relative to each other about a common axis. The lower block is driven to pull wire through a die, with the thus drawn wire then being accumulated temporarily as a plurality of windings on the lower block. The wire then passes from the lower block via the spinner-mounted transfer sheave to the upper block where it is again temporarily accumulated as a plurality of windings before leaving the station to either be passed through a subsequent die or to be finally accumulated on a spool as finished wire.
In order to control the tension of the wire passing between the lower and upper blocks, the spinner is driven, either by an externally contracting drive band which frictionally grips the lower block, or by a motor driving through a V-belt. The direction of rotation of the upper block is either opposite to that of the lower block, or non-existent, depending on whether the blocks are accumulating. The spinner may rotate in either direction, or it may remain motionless.
The rate of wire accumulation on the blocks varies according to the relative drafting practice between stations. While the spinner is motionless, the lower block is passing wire around the transfer sheave and onto the upper block as fast as the wire is coming onto the lower block, and the upper block is passing wire to the next station as fast as it is being received from the lower block. If the succeeding station requires more wire than is being supplied to the lower block, it will pull accumulated wire from the upper block, which in turn will pull accumulated wire from the lower block. However, only one-half the amount required will be pulled from the lower block's accumulation. The other half will be made up from the upper block's accumulation through rotation of the spinner. The wire accumulation is being decreased during this type of operation, with the spinner being rotatably driven in a direction opposite to that of the lower block.
When the succeeding station demands less wire than that being drawn into the lower block, there will be an excess of wire being passed from the lower block to the upper block. In this case, the spinner is rotatably driven in the same direction as that of the lower block, thereby causing one-half of the excess accumulation to go to the lower block and one-half to go to the upper block.
Although this type of machine operates in a generally satisfactory manner, difficulties have been experienced with the manner in which the spinners are driven. For example, the externally contracting drive bands can be adjusted only when the machine is stopped. Thus, tension control of the wire passing from the lower to the upper blocks is largely a matter of trial and error with each adjustment necessitating a machine shutdown. While the V-belt drive offers an improvement in this respect in that it can be adjusted to control tension while the machine is in operation, because the belt is located externally of the blocks, it is exposed to the path of wire movement and is frequently severed when a wire break occurs. Thus, both spinner driving systems are a source of problems.